LM13700
The LM13700 in an operational transconductance amplifier, or OTA for short. The lm13700 is almost identical to the LM13600, except that the darlington output buffer is biased by the IABC input on the 13600. The LM13700 is like a standard op-amp: both have a pair of differential inputs and a single output, but an OTA is voltage in and current out rather than voltage in and voltage out; and OTAs are programmable via the IABC pin. This chip is very useful in audio electronics especially in analog synthesizer circuits like voltage controlled oscillators, voltage controlled filters, and voltage controlled amplifiers. The OTA chip utilizes a differential input stage and current mirrors to to achieve its unique circuit characteristics.